Method and system for homogenizing the delivery of fuels in a gasifier for generating syngas

ABSTRACT

A method and a system for uniformization and regulation of the solid fuels pneumatically conveyed using dense-stream conveying, into a gasifier for the production of synthesis gas, is supposed to be configured in such a manner that clearly homogenized feed of the coal to the burner is made possible, whereby the short-term fluctuations are minimized and thus the gasification quality is improved, and regulation of the amounts of coal to the burner is structured to be more effective. This is achieved in that the fine-grain to dust-type fuel is first conveyed out of a feed container positioned below the burner level, to a level above the burner level, and subsequently homogenized in a line that is directed downward toward the burner.

The invention is directed at a method for uniformization and regulationof the solid fuels pneumatically conveyed using dense-stream conveying,into a gasifier for the production of synthesis gas.

Regulated feed of fuel dust in an entrained-flow gasifier is described,for example, in DE 10 2005 047 583 A. In this connection, it is known toreact the fuel using the burners that are built into the verticalgasifier wall and are essentially oriented horizontally, whereby thefuel, composed of finely distributed or dust-type (<0.5 mm) fuelparticles, for example coke, petro-coke, biological waste, and otherfuels, is reacted with gasification agents that contain oxygen, underelevated pressure, at temperatures above the slag melting point.

A device and a method for pneumatic conveying of bulk materials, usingthe dense-stream method, are known from WO 2006/015702 A1.

In the implementation of pressurized gasification processes, acarbonaceous fuel is reacted with a gas that contains oxygen, wherebythe gas that contains oxygen is fed in the sub-stoichiometric ratio, sothat a product gas that contains hydrogen and carbon monoxide isobtained. In order to achieve a high rate of reaction of the fuel and ahigh degree of efficiency, the fuel/oxygen ratio must be adjusted withina narrow range.

In pressurized gasification, burners having coaxial channels aregenerally used, whereby mixing of the media being fed in takes place notin the burner, but only in the gasifier. An example of a burner used ina pressurized gasification system is presented in detail in EP 0 437 698A1, for example. Supply of the burners with fuel usually takes placefrom a feed container that stands slightly above gasifier pressure, bymeans of dense-stream conveying. In this connection, pneumatic conveyingis referred to as dense-stream conveying, whereby the carrier gastransports the fuel particles not as individual particles, but rather inthe form of dense fillings or plugs that fill the entire pipecross-section. In general, dense-stream conveying deliveries possessspeeds of 4 to 6 m/s, whereby the high solids charge of the gas streamnevertheless leads to a high transport amount. Dense-stream conveying isvery gentle on the material and, above all, is not very susceptible tobreak-down with regard to sticky or damp transport material.

The quality of gasification is decisively influenced by the uniformityof the coal feed to the burner. While variations over longer timeintervals (for example due to planned regulation measures or due to achange in the coal used, etc.) are determined by means of measurementtechnology and taken into consideration, very short-term fluctuations inthe feed quality (feed density and velocity) cannot be compensated.

Since dense-stream conveying involves a fluidized gas/solid mixture, inthe broadest sense, here, too, the fluctuations in density and velocitythat are typical for a fluidized bed can be observed. These can only beinfluenced by means of indirect measures, such as the configuration ofthe feed into the feed line. For this purpose, it is furthermore knownthat settling phenomena of the solid can occur in long horizontalsections of the feed line, and this is usually minimized by means of thefeed of additional gas. Further homogenization is achieved when the lineleads upward once again.

Because of the space requirements and the system-specific setup, thesituation usually is that the feed container that supplies the burnersby way of a feed line is situated “at the bottom” in the systemstructure, while the burners are situated at a clearly higher level,because of the vertical method of construction of the gasifier. Setup ofthe feed container “at the bottom” is cost-advantageous, particularly ifthe required fuel transport into the feed container is based on gravityflow and therefore has to be positioned above the feed container.

Until now, the line placement of the feed line to the burners went from“the bottom” to “the top” at burner level, and there was ledhorizontally to the connector taps of the burner, in most cases, fromwhere the coal went into the burner.

It is the task of the present invention to configure a method asdescribed initially in such a manner that clearly homogenized feed ofthe coal to the burner is made possible, whereby the short-termfluctuations are minimized, and thus the gasification quality isimproved, and regulation of the amounts of coal to the burner isstructured more effectively.

This task is accomplished, according to the invention, with a method ofthe type mentioned initially, in that the fine-grain to dust-type fuelis first conveyed out of a feed container positioned below the burnerlevel, to a level above the burner level, and subsequently homogenizedin a line that is directed downward toward the burner.

It has been shown that uniformity of the fuel/gas mixture transported inthe dense stream is achieved by means of the method of operationaccording to the invention, which uniformity is clearly better thanconveying through lines that run horizontally. Because of thehomogenization in the drop line ahead of the burner, the fuel particlesare accelerated by gravity, whereby gas bubbles that might be containedin the mixture are filled with fuel as the mixture drops.

Embodiments are evident from the dependent claims. In this connection,it can be provided that the homogenization takes place in a line that isdirected downward, whose length corresponds to at least five times theline diameter.

It has proven to be practical if the fuel is homogenized in a drop linethat is passed out of an elbow, whereby the drop line is oriented atangles <20°, preferably at 0° from the vertical.

However, the range in which the drop line can be adjusted relative tothe vertical can also be selected to be different from what is claimedhere, depending on the material that is being used; the decisive factoris the homogenization in the drop pipe.

Another practical embodiment according to the invention consists in thatgas is fed into the fuel stream, to regulate the fuel throughput,whereby mixing is undertaken just before or in the burner.

Dilution is brought about by adding auxiliary gas into the fuel streambeing conveyed as a dense stream, in other words the conveying densityis reduced. While the velocity of the diluted fuel is increased, theinfluence of the reduced density nevertheless predominates, whereby thethroughput is reduced.

EXAMPLE

10 kg/s fuel having a density of 400 kg/m³ and a velocity of 5 m/s areconveyed through a burner into the gasifier, using dense-streamconveying. Because of friction and upward conveying, a pressure loss of100 kPa occurs in the pipeline. In the burner, a pressure loss of 20 kPaoccurs due to friction and further acceleration of the suspension. Inorder to reduce the throughput, auxiliary gas is fed into the fuel linedirectly ahead of the burner, thereby almost doubling the volume stream.The pressure loss in the fuel channel of the burner is also doubled as aresult. Since the fuel channel is only 2 m long, it is filled with thediluted fuel after only 0.2 s. The fuel throughput is already reducedafter this short period of time.

The example shows that very rapid adaptation of the fuel throughput ispossible. However, the regulation range is restricted by the requiredamount of gas and the fuel velocity in the burner, which is restricteddue to erosion. With this method, the fuel throughput can be changed by+/−10% in a typical application.

The invention will be explained in greater detail below, using thedrawing as an example. This shows, in

FIG. 1 a schematic layer diagram, as well as in

FIG. 2 an enlarged detail in the area of a burner, not shown in greaterdetail, in an indicated gasifier wall.

FIG. 1 shows the dense-stream conveying 2 a and 2 b out of the feedcontainer 1 into the burners 4 a, 4 b of the gasifier 3. The exit of thefeed container is lower than the burners, so that the fuel should beconveyed horizontally and upward. However, in order to achieve ahomogeneous fuel suspension, the fuel is first passed to above burnerlevel, and then, after deflection, homogenized in a drop line having alength of 3 m, for example. Just ahead of the burner, the lines aredeflected, in order to feed the fuel into the burners horizontally, andauxiliary gas 11 a, 11 b is fed into the line. Also, a gas 5 a, 5 b thatcontains oxygen and a moderation gas 6 a, 6 b are fed into the burner,and these influence the gasification parameters.

Alternatively, the auxiliary gas 11 a, 11 b can be fed directly into theburner or into the fuel channel of the burner.

FIG. 2 shows an alternative embodiment of the method. Dense-streamconveying 2 is passed into the vertical drop line in an arc. Ahead ofthe burner tap 12, which is oriented vertically, an auxiliary gas 11 orpart of the moderation gas 6, for example CO₂, is fed into the gasintroduction device 10, in order to reduce the conveying density and thefuel stream.

1: Method for uniformization and regulation of the solid fuelspneumatically conveyed using dense-stream conveying, into a gasifier forthe production of synthesis gas, whereby the fine-grain to dust-typefuel is first conveyed out of a feed container positioned below theburner level, to a level above the burner level, and subsequentlyhomogenized in a line that is directed downward toward the burner,wherein gas is fed into the fuel stream, to regulate the fuelthroughput, whereby mixing is undertaken just before or in the burner,and wherein for temperature regulation, in particular, at least a partof the gas used in the gasifier (moderation gas) is introduced into theconveyed fuel. 2: Method according to claim 1, wherein thehomogenization takes place in a line that is directed downward, thelength of which line corresponds to at least five times the linediameter. 3: Method according to claim 1, wherein the fuel ishomogenized in a drop line that is passed out of an elbow, whereby thedrop line is oriented at angles <20°, preferably at 0° from thevertical. 4-5. (canceled) 6: Method according to claim 1, whereinadditional gas, such as nitrogen, carbon dioxide, steam, other inertgases or mixtures of them, is used. 7: Method according to claim 6,wherein the additional gas is introduced by way of a pipe tap, in theimmediate vicinity of the burner. 8: System for uniformization andregulation of the solid fuels pneumatically conveyed using dense-streamconveying, into a gasifier (3) for the production of synthesis gas,particularly for carrying out the method according to claim 1, furthercomprising dense-stream conveying lines (2, 2 a, 2 b) from a feedcontainer (1) to the burners (4, 4 a, 4 b) of the gasifier (3), wherebythe end region of the dense-stream conveying line (2) is positionedperpendicular ahead of the burner (4), in each instance. 9: Systemaccording to claim 8, wherein the length of the perpendiculardense-stream line section corresponds to at least five times thedense-stream line diameter.